<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>我想访问4000端口</button>
    <script>
        let btn=document.querySelector('button')
        btn.onclick=function(){
            let xhr=new XMLHttpRequest()
            xhr.open('get','http://localhost:4000/getdata')
            xhr.send()
            xhr.onload=function(res){
                console.log(xhr.responseText);
            }
        }
    </script>
</body>
</html>